Method of fabricating printhead assembly

ABSTRACT

A printhead assembly includes a molded ink manifold, a plurality of printhead integrated circuits, and an adhesive film sandwiched between the ink manifold and the printhead integrated circuits. A manifold bonding surface of the molded ink manifold includes a polymer coating. The polymer coating plugs fissures resulting from a molding process used to mold the ink manifold.

FIELD OF THE INVENTION

The present invention relates to printers and in particular inkjetprinters.

CO-PENDING APPLICATIONS

The following application has been filed by the Applicant simultaneouslywith the present application:

RRE055US

The disclosure of this co-pending application is incorporated herein byreference. The above application has been identified by its filingdocket number, which will be substituted with the correspondingapplication number, once assigned.

CROSS REFERENCES

The following patents or patent applications filed by the applicant orassignee of the present invention are hereby incorporated bycross-reference.

7,344,226 7,328,976 11/685,084 11/685,086 11/685,090 11/740,92511/763,444 11/763,443 11/946,840 7,441,879 12/017,771 12/205,90812/264,903 12/265,637 12/323,471 12/323,472 12/323,473 11/607,9767,416,280 7,278,717 6,755,509 7,347,537 6,692,108 7,407,271 6,672,7097,303,263 7,086,718 7,429,097 6,672,710 10/534,812 6,669,334 7,322,6867,152,958 7,281,782 6,824,246 7,264,336 6,669,333 7,357,489 6,820,9677,306,326 6,736,489 7,264,335 6,719,406 7,222,943 7,188,419 7,168,1666,974,209 7,086,719 6,974,210 7,195,338 7,252,775 7,101,025 11/474,28111/485,258 11/706,304 11/706,324 11/706,326 11/706,321 11/772,2397,401,903 7,416,284 11/852,991 11/852,986 7,441,876 11/934,02711/955,028 12/034,578 12/036,908 12/140,198 12/141,079 12/172,94012/190,462 12/206,679 12/246,332 12/246,336 12/272,725 12/276,36211/763,440 11/763,442 12/114,826 12/114,827 12/239,814 12/239,81512/239,816 7,448,734 7,425,050 7,364,263 7,201,468 7,360,868 10/760,2497,234,802 7,303,255 7,287,846 7,156,511 10/760,264 7,258,432 7,097,29110/760,222 10/760,248 7,083,273 7,367,647 7,374,355 7,441,880 10/760,20510/760,206 10/760,267 10/760,270 7,198,352 7,364,264 7,303,251 7,201,4707,121,655 7,293,861 7,232,208 7,328,985 7,344,232 7,083,272 7,311,38711/583,874 7,303,258 11/706,322 11/706,968 11/749,119 11/779,84811/855,152 11/855,151 11/870,327 11/934,780 11/935,992 11/951,19312/017,327 12/015,273 12/036,882 12/050,164 12/050,166 12/062,50212/103,710 12/186,489 12/205,890 12/234,695 11/014,764 11/014,7637,331,663 7,360,861 7,328,973 7,427,121 7,407,262 7,303,252 7,249,82211/014,762 7,311,382 7,360,860 7,364,257 7,390,075 7,350,896 7,429,0967,384,135 7,331,660 7,416,287 11/014,737 7,322,684 7,322,685 7,311,3817,270,405 7,303,268 11/014,735 7,399,072 7,393,076 11/014,750 11/014,7497,249,833 11/758,640 11/775,143 11/838,877 11/944,453 11/944,63311/955,065 12/003,875 12/003,952 12/007,818 12/007,817 12/068,67912/071,187 12/076,666 12/076,665 12/076,664 12/079,897 12/122,71212/138,418 12/138,420 12/138,424 12/123,371 12/123,394 12/123,40312/170,431 12/177,864 12/177,866 12/177,868 12/177,871 12/190,56112/276,404 12/276,384 12/276,358 11/014,769 11/014,729 7,331,66111/014,733 7,300,140 7,357,492 7,357,493 11/014,766 7,380,902 7,284,8167,284,845 7,255,430 7,390,080 7,328,984 7,350,913 7,322,671 7,380,9107,431,424 11/014,716 11/014,732 7,347,534 7,441,865 11/097,185 7,367,65011/778,567 11/852,958 11/852,907 11/872,038 11/955,093 11/961,57812/022,023 12/023,000 12/023,018 12/031,582 12/043,708 12/101,15012/121,792 12/122,711 12/138,417 12/194,536 12/206,740 12/264,00112/264,126 12/324,573 12/273,392 11/293,820 7,441,882 11/293,82211/293,812 7,357,496 11/293,814 7,431,440 7,431,443 11/293,81111/293,807 11/293,806 11/293,805 11/293,810 12/050,021 12/145,50512/199,687 12/194,539 12/233,589 12/266,204 12/272,716 12/273,45612/276,405 11/688,863 11/688,864 11/688,865 7,364,265 11/688,86711/688,868 11/688,869 11/688,871 11/688,872 11/688,873 11/741,76612/014,767 12/014,768 12/014,769 12/014,770 12/014,771 12/014,77212/014,773 12/014,774 12/014,775 12/014,776 12/014,777 12/014,77812/014,779 12/014,780 12/014,781 12/014,782 12/014,783 12/014,78412/014,785 12/014,787 12/014,788 12/014,789 12/014,790 12/014,79112/014,792 12/014,793 12/014,794 12/014,796 12/014,798 12/014,80112/014,803 12/014,804 12/014,805 12/014,806 12/014,807 12/049,37112/049,372 12/049,373 12/049,374 12/049,375 12/103,674 12/146,39912/276,400 11/482,982 11/482,983 11/482,984 11/495,818 11/495,81911/677,049 11/677,050 11/677,051 11/872,719 11/872,718 12/046,44912/062,514 12/062,517 12/062,518 12/062,520 12/062,521 12/062,52212/062,523 12/062,524 12/062,525 12/062,526 12/062,527 12/062,52812/062,529 12/062,530 12/062,531 12/192,116 12/192,117 12/192,11812/192,119 12/192,120 12/192,121

BACKGROUND OF THE INVENTION

The Applicant has developed a wide range of printers that employpagewidth printheads instead of traditional reciprocating printheaddesigns. Pagewidth designs increase print speeds as the printhead doesnot traverse back and forth across the page to deposit a line of animage. The pagewidth printhead simply deposits the ink on the media asit moves past at high speeds. Such printheads have made it possible toperform full colour 1600 dpi printing at speeds in the vicinity of 60pages per minute, speeds previously unattainable with conventionalinkjet printers.

Printing at these speeds consumes ink quickly and this gives rise toproblems with supplying the printhead with enough ink. Not only are theflow rates higher but distributing the ink along the entire length of apagewidth printhead is more complex than feeding ink to a relativelysmall reciprocating printhead.

Printhead integrated circuits are typically attached to an ink manifoldusing an adhesive film. It would be desirable to optimize thisattachment process so as to provide a printhead assembly exhibitingminimal ink leakages.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a printhead assemblycomprising:

-   -   a molded ink manifold having a plurality of ink outlets defined        in a manifold bonding surface;    -   one or more printhead integrated circuits, each printhead        integrated circuit having one or more ink inlets defined in a        printhead bonding surface; and    -   an adhesive film sandwiched between the manifold bonding surface        and the one or more printhead bonding surfaces, the film having        a plurality of ink supply holes defined therein, each ink supply        hole being aligned with an ink outlet and an ink inlet,        wherein at least the manifold bonding surface comprises a        polymer coating, the polymer coating plugging fissures in the        molded ink manifold.

The printhead assembly according to the first aspect advantageouslyminimizes ink leakages by plugging microscopic molding fissures in themolded ink manifold.

Optionally, the fissures are unwanted fissures resulting from a moldingprocess used to fabricate the ink manifold. Some unwanted microscopicfissures are typically inevitable, even when using high tolerancemolding tools.

Optionally, the manifold bonding surface is substantially planar as aresult of the polymer coating plugging the fissures. A planar manifoldbonding surface advantageously minimizes ink leakages through moldingfissures in the bonding surface.

Optionally, the entire molded ink manifold is coated with the polymercoating. Accordingly, all molding fissures, including internal fissuresbetween ink supply passages in the molded ink manifold, may be plugged.

Optionally, the polymer coating is selected from the group of polymersconsisting of: polyimides, polyesters, epoxies, polyolefins, siloxanesand liquid crystal polymers. The polymer coating is typically differentfrom a polymer used to form the molded ink manifold.

Optionally, the polymer coating comprises inorganic or organic additivesfor providing one or more of the following characteristics: wettability,adhesive bond strength, and scratch-resistance. Hence, the polymercoating may advantageously have multiple functions, in addition to itsprimary function of plugging fissures. For example, silica particulatesmay be incorporated into the polymer coating to improve durability,scratch-resistance, wettability etc.

Optionally, the polymer coating is applied to the molded ink manifold bydipping, spray coating or spin coating.

Optionally, a plurality of printhead integrated circuits are butted endon end along a longitudinal extent of the ink supply manifold. Thisarrangement for fabricating printheads has been described by the presentApplicant in the cross-reference patents and patent applicationsincorporated herein by reference.

Optionally, the plurality of printhead integrated circuits define apagewidth printhead.

Optionally, a plurality of ink inlets are defined by an ink supplychannel extending longitudinally along the printhead bonding surface.Optionally, a plurality of ink supply holes are aligned with one inksupply channel, each of the plurality of ink supply holes being spacedapart longitudinally along the ink supply channel.

In a second aspect, there is provided a pagewidth printer comprising astationary printhead assembly as described above.

In a third aspect, there is provided a molded ink manifold for an inkjetprinthead, the ink manifold having a manifold bonding surface forattachment of one or more printhead integrated circuits, each of theprinthead integrated circuits receiving ink from one or more ink outletsdefined in the bonding surface, wherein at least the manifold bondingsurface comprises a polymer coating, the polymer coating pluggingfissures in the molded ink manifold.

In a fourth aspect, there is provided a method of fabricating aprinthead assembly, the method comprising the steps of:

(i) providing a molded ink manifold having a manifold bonding surfacefor attachment of one or more printhead integrated circuits, the bondingsurface having a plurality of ink outlets defined therein, the bondingsurface having a plurality of fissures resulting from a molding process;

(ii) coating at least the manifold bonding surface with a polymercoating, thereby plugging the fissures; and

(iii) bonding one or more printhead integrated circuits to the manifoldbonding surface.

Optionally, the manifold bonding surface is substantially planar as aresult of the polymer coating plugging the fissures.

Optionally, the coating step coats the entire molded ink manifold withthe polymer coating.

Optionally, the polymer coating plugs internal fissures between inksupply passages defined in the ink manifold.

Optionally, the polymer coating is selected from the group of polymersconsisting of: polyimides, polyesters, epoxies, polyolefins, siloxanesand liquid crystal polymers.

Optionally, the polymer coating comprises inorganic or organic additivesfor providing one or more of the following characteristics: wettability,adhesive bond strength, and scratch-resistance.

Optionally, the coating step comprises any one of: dipping, spraycoating or spin coating.

Optionally, the coating step utilizes a polymer coating solutioncomprising an organic solvent.

Optionally, the coating step is controlled to provide a polymer coatinghaving a predetermined thickness. The thickness of the polymer coatingmay be controlled by parameters, such as dipping time and polymerviscosity.

Optionally, the bonding step comprises:

-   bonding an adhesive film to the manifold bonding surface; and-   bonding the printhead integrated circuits to the adhesive film.

Optionally, the adhesive film is a laminated film comprising a centralpolymeric film sandwiched between first and second adhesive layers.

In a fifth aspect, there is provided a bonded printhead assemblycomprising one or more printhead integrated circuits bonded to manifoldbonding surface of a molded ink supply manifold, wherein the manifoldbonding surface comprises a polymer coating, the polymer coatingplugging a plurality of fissures in the molded ink manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings, in which:

FIG. 1 is a front and side perspective of a printer embodying thepresent invention;

FIG. 2 shows the printer of FIG. 1 with the front face in the openposition;

FIG. 3 shows the printer of FIG. 2 with the printhead cartridge removed;

FIG. 4 shows the printer of FIG. 3 with the outer housing removed;

FIG. 5 shows the printer of FIG. 3 with the outer housing removed andprinthead cartridge installed;

FIG. 6 is a schematic representation of the printer's fluidic system;

FIG. 7 is a top and front perspective of the printhead cartridge;

FIG. 8 is a top and front perspective of the printhead cartridge in itsprotective cover;

FIG. 9 is a top and front perspective of the printhead cartridge removedfrom its protective cover;

FIG. 10 is a bottom and front perspective of the printhead cartridge;

FIG. 11 is a bottom and rear perspective of the printhead cartridge;

FIG. 12 shows the elevations of all sides of the printhead cartridge;

FIG. 13 is an exploded perspective of the printhead cartridge;

FIG. 14 is a transverse section through the ink inlet coupling of theprinthead cartridge;

FIG. 15 is an exploded perspective of the ink inlet and filter assembly;

FIG. 16 is a section view of the cartridge valve engaged with theprinter valve;

FIG. 17 is a perspective of the LCP molding and flex PCB;

FIG. 18 is an enlargement of inset A shown in FIG. 17;

FIG. 19 is an exploded bottom perspective of the LCP/flex PCB/printheadIC assembly;

FIG. 20 is an exploded top perspective of the LCP/flex PCB/printhead ICassembly;

FIG. 21 is an enlarged view of the underside of the LCP/flexPCB/printhead IC assembly;

FIG. 22 shows the enlargement of FIG. 21 with the printhead ICs and theflex PCB removed;

FIG. 23 shows the enlargement of FIG. 22 with the printhead IC attachfilm removed;

FIG. 24 shows the enlargement of FIG. 23 with the LCP channel moldingremoved;

FIG. 25 shows the printhead ICs with back channels and nozzlessuperimposed on the ink supply passages;

FIG. 26 in an enlarged transverse perspective of the LCP/flexPCB/printhead IC assembly;

FIG. 27 is a plan view of the LCP channel molding;

FIGS. 28A and 28B are schematic section views of the LCP channel moldingpriming without a weir;

FIGS. 29A, 29B and 29C are schematic section views of the LCP channelmolding priming with a weir;

FIG. 30 in an enlarged transverse perspective of the LCP molding withthe position of the contact force and the reaction force;

FIG. 31 shows a reel of the IC attachment film;

FIG. 32 shows a section of the IC attach film between liners;

FIG. 33A-C are partial sections showing various stages of traditionallaser-drilling of an attachment film;

FIGS. 34A-C are partial sections showing various stages of doublelaser-drilling of an attachment film;

FIGS. 35A-D are longitudinal sections of a schematic printhead ICattachment process;

FIGS. 36A and 36B are photographs of ink supply holes in two differentattachment films after a first bonding step;

FIGS. 37A and 37B are longitudinal sections of a schematic printhead ICattachment process;

FIG. 38 shows schematically a printhead assembly with exaggeratedfissures in a molded ink manifold;

FIG. 39 shows schematically a process for applying a polymer coating tothe molded ink manifold; and

FIG. 40 shows schematically a printhead assembly having pluggedfissures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Overview

FIG. 1 shows a printer 2 embodying the present invention. The main body4 of the printer supports a media feed tray 14 at the back and apivoting face 6 at the front. FIG. 1 shows the pivoting face 6 closedsuch that the display screen 8 is its upright viewing position. Controlbuttons 10 extend from the sides of the screen 8 for convenient operatorinput while viewing the screen. To print, a single sheet is drawn fromthe media stack 12 in the feed tray 14 and fed past the printhead(concealed within the printer). The printed sheet 16 is deliveredthrough the printed media outlet slot 18.

FIG. 2 shows the pivoting front face 6 open to reveal the interior ofthe printer 2. Opening the front face of the printer exposes theprinthead cartridge 96 installed within. The printhead cartridge 96 issecured in position by the cartridge engagement cams 20 that push itdown to ensure that the ink coupling (described later) is fully engagedand the printhead ICs (described later) are correctly positionedadjacent the paper feed path. The cams 20 are manually actuated by therelease lever 24. The front face 6 will not close, and hence the printerwill not operate, until the release lever 24 is pushed down to fullyengage the cams. Closing the pivoting face 6 engages the printercontacts 22 with the cartridge contacts 104.

FIG. 3 shows the printer 2 with the pivoting face 6 open and theprinthead cartridge 96 removed. With the pivoting face 6 tilted forward,the user pulls the cartridge release lever 24 up to disengage the cams20. This allows the handle 26 on the cartridge 96 to be gripped andpulled upwards. The upstream and downstream ink couplings 112A and 112Bdisengage from the printer conduits 142. This is described in greaterdetail below. To install a fresh cartridge, the process is reversed. Newcartridges are shipped and sold in an unprimed condition. So to readythe printer for printing, the active fluidics system (described below)uses a downstream pump to prime the cartridge and printhead with ink.

In FIG. 4, the outer casing of the printer 2 has been removed to revealthe internals. A large ink tank 60 has separate reservoirs for all fourdifferent inks. The ink tank 60 is itself a replaceable cartridge thatcouples to the printer upstream of the shut off valve 66 (see FIG. 6).There is also a sump 92 for ink drawn out of the cartridge 96 by thepump 62. The printer fluidics system is described in detail withreference to FIG. 6. Briefly, ink from the tank 60 flows through theupstream ink lines 84 to the shut off valves 66 and on to the printerconduits 142. As shown in FIG. 5, when the cartridge 96 is installed,the pump 62 (driven by motor 196) can draw ink into the LCP molding 64(see FIGS. 6 and 17 to 20) so that the printhead ICs 68 (again, seeFIGS. 6 and 17 to 20) prime by capillary action. Excess ink drawn by thepump 62 is fed to a sump 92 housed with the ink tanks 60.

The total connector force between the cartridge contacts 104 and theprinter contacts 22 is relatively high because of the number of contactsused. In the embodiment shown, the total contact force is 45 Newtons.This load is enough to flex and deform the cartridge. Turning briefly toFIG. 30, the internal structure of the chassis molding 100 is shown. Thebearing surface 28 shown in FIG. 3 is schematically shown in FIG. 30.The compressive load of the printer contacts on the cartridge contacts104 is represented with arrows. The reaction force at the bearingsurface 28 is likewise represented with arrows. To maintain thestructural integrity of the cartridge 96, the chassis molding 100 has astructural member 30 that extends in the plane of the connector force.To keep the reaction force acting in the plane of the connector force,the chassis also has a contact rib 32 that bears against the bearingsurface 28. This keeps the load on the structural member 30 completelycompressive to maximize the stiffness of the cartridge and minimize anyflex.

Print Engine Pipeline

The print engine pipeline is a reference to the printer's processing ofprint data received from an external source and outputted to theprinthead for printing. The print engine pipeline is described in detailin U.S. Ser. No. 11/014,769 filed Dec. 20, 2004, the disclosure of whichis incorporated herein by reference.

Fluidic System

Traditionally printers have relied on the structure and componentswithin the printhead, cartridge and ink lines to avoid fluidic problems.Some common fluidic problems are deprimed or dried nozzles, outgassingbubble artifacts and color mixing from cross contamination. Optimizingthe design of the printer components to avoid these problems is apassive approach to fluidic control. Typically, the only activecomponent used to correct these were the nozzle actuators themselves.However, this is often insufficient and or wastes a lot of ink in theattempt to correct the problem. The problem is exacerbated in pagewidthprintheads because of the length and complexity of the ink conduitssupplying the printhead ICs.

The Applicant has addressed this by developing an active fluidic systemfor the printer. Several such systems are described in detail in U.S.Ser. No. 11/677,049 the contents of which are incorporated herein byreference. FIG. 6 shows one of the single pump implementations of theactive fluidic system which would be suitable for use with the printheaddescribed in the present specification.

The fluidic architecture shown in FIG. 6 is a single ink line for onecolor only. A color printer would have separate lines (and of courseseparate ink tanks 60) for each ink color. As shown in FIG. 6, thisarchitecture has a single pump 62 downstream of the LCP molding 64, anda shut off valve 66 upstream of the LCP molding. The LCP moldingsupports the printhead IC's 68 via the adhesive IC attach film 174 (seeFIG. 25). The shut off valve 66 isolates the ink in the ink tank 60 fromthe printhead IC's 66 whenever the printer is powered down. Thisprevents any color mixing at the printhead IC's 68 from reaching the inktank 60 during periods of inactivity. These issues are discussed in moredetail in the cross referenced specification U.S. Ser. No. 11/677,049.

The ink tank 60 has a venting bubble point pressure regulator 72 formaintaining a relatively constant negative hydrostatic pressure in theink at the nozzles. Bubble point pressure regulators within inkreservoirs are comprehensively described in co-pending U.S. Ser. No.11/640,355 incorporated herein by reference. However, for the purposesof this description the regulator 72 is shown as a bubble outlet 74submerged in the ink of the tank 60 and vented to atmosphere via sealedconduit 76 extending to an air inlet 78. As the printhead IC's 68consume ink, the pressure in the tank 60 drops until the pressuredifference at the bubble outlet 74 sucks air into the tank. This airforms a forms a bubble in the ink which rises to the tank's headspace.This pressure difference is the bubble point pressure and will depend onthe diameter (or smallest dimension) of the bubble outlet 74 and theLaplace pressure of the ink meniscus at the outlet which is resistingthe ingress of the air.

The bubble point regulator uses the bubble point pressure needed togenerate a bubble at the submerged bubble outlet 74 to keep thehydrostatic pressure at the outlet substantially constant (there areslight fluctuations when the bulging meniscus of air forms a bubble andrises to the headspace in the ink tank). If the hydrostatic pressure atthe outlet is at the bubble point, then the hydrostatic pressure profilein the ink tank is also known regardless of how much ink has beenconsumed from the tank. The pressure at the surface of the ink in thetank will decrease towards the bubble point pressure as the ink leveldrops to the outlet. Of course, once the outlet 74 is exposed, the headspace vents to atmosphere and negative pressure is lost. The ink tankshould be refilled, or replaced (if it is a cartridge) before the inklevel reaches the bubble outlet 74.

The ink tank 60 can be a fixed reservoir that can be refilled, areplaceable cartridge or (as disclosed in RRC001US incorporated byreference) a refillable cartridge. To guard against particulate fouling,the outlet 80 of the ink tank 60 has a coarse filter 82. The system alsouses a fine filter at the coupling to the printhead cartridge. Asfilters have a finite life, replacing old filters by simply replacingthe ink cartridge or the printhead cartridge is particularly convenientfor the user. If the filters are separate consumable items, regularreplacement relies on the user's diligence.

When the bubble outlet 74 is at the bubble point pressure, and the shutoff valve 66 is open, the hydrostatic pressure at the nozzles is alsoconstant and less than atmospheric. However, if the shut off valve 66has been closed for a period of time, outgassing bubbles may form in theLCP molding 64 or the printhead IC's 68 that change the pressure at thenozzles. Likewise, expansion and contraction of the bubbles from diurnaltemperature variations can change the pressure in the ink line 84downstream of the shut off valve 66. Similarly, the pressure in the inktank can vary during periods of inactivity because of dissolved gasescoming out of solution.

The downstream ink line 86 leading from the LCP 64 to the pump 62 caninclude an ink sensor 88 linked to an electronic controller 90 for thepump. The sensor 88 senses the presence or absence of ink in thedownstream ink line 86. Alternatively, the system can dispense with thesensor 88, and the pump 62 can be configured so that it runs for anappropriate period of time for each of the various operations. This mayadversely affect the operating costs because of increased ink wastage.

The pump 62 feeds into a sump 92 (when pumping in the forwarddirection). The sump 92 is physically positioned in the printer so thatit is less elevated than the printhead ICs 68. This allows the column ofink in the downstream ink line 86 to ‘hang’ from the LCP 64 duringstandby periods, thereby creating a negative hydrostatic pressure at theprinthead ICs 68. A negative pressure at the nozzles draws the inkmeniscus inwards and inhibits color mixing. Of course, the peristalticpump 62 needs to be stopped in an open condition so that there is fluidcommunication between the LCP 64 and the ink outlet in the sump 92.

Pressure differences between the ink lines of different colors can occurduring periods of inactivity. Furthermore, paper dust or otherparticulates on the nozzle plate can wick ink from one nozzle toanother. Driven by the slight pressure differences between each inkline, color mixing can occur while the printer is inactive. The shut offvalve 66 isolates the ink tank 60 from the nozzle of the printhead IC's68 to prevent color mixing extending up to the ink tank 60. Once the inkin the tank has been contaminated with a different color, it isirretrievable and has to be replaced.

The capper 94 is a printhead maintenance station that seals the nozzlesduring standby periods to avoid dehydration of the printhead ICs 68 aswell as shield the nozzle plate from paper dust and other particulates.The capper 94 is also configured to wipe the nozzle plate to removedried ink and other contaminants. Dehydration of the printhead ICs 68occurs when the ink solvent, typically water, evaporates and increasesthe viscosity of the ink. If the ink viscosity is too high, the inkejection actuators fail to eject ink drops. Should the capper seal becompromised, dehydrated nozzles can be a problem when reactivating theprinter after a power down or standby period.

The problems outlined above are not uncommon during the operative lifeof a printer and can be effectively corrected with the relatively simplefluidic architecture shown in FIG. 6. It also allows the user toinitially prime the printer, deprime the printer prior to moving it, orrestore the printer to a known print ready state using simpletrouble-shooting protocols. Several examples of these situations aredescribed in detail in the above referenced U.S. Ser. No. 11/677,049.

Printhead Cartridge

The printhead cartridge 96 is shown in FIGS. 7 to 16A. FIG. 7 shows thecartridge 96 in its assembled and complete form. The bulk of thecartridge is encased in the cartridge chassis 100 and the chassis lid102. A window in the chassis 100 exposes the cartridge contacts 104 thatreceive data from the print engine controller in the printer.

FIGS. 8 and 9 show the cartridge 96 with its snap on protective cover98. The protective cover 98 prevents damaging contact with theelectrical contacts 104 and the printhead IC's 68 (see FIG. 10). Theuser can hold the top of the cartridge 96 and remove the protectivecover 98 immediately prior to installation in the printer.

FIG. 10 shows the underside and ‘back’ (with respect to the paper feeddirection) of the printhead cartridge 96. The printhead contacts 104 areconductive pads on a flexible printed circuit board 108 that wrapsaround a curved support surface (discussed below in the descriptionrelating to the LCP moulding) to a line of wire bonds 110 at one side ifthe printhead IC's 68. On the other side of the printhead IC's 68 is apaper shield 106 to prevent direct contact with the media substrate.

FIG. 11 shows the underside and the ‘front’ of the printhead cartridge96. The front of the cartridge has two ink couplings 112A and 112B ateither end. Each ink coupling has four cartridge valves 114. When thecartridge is installed in the printer, the ink couplings 112A and 112Bengage complementary ink supply interfaces (described in more detailbelow). The ink supply interfaces have printer conduits 142 which engageand open the cartridge valves 114. One of the ink couplings 112A is theupstream ink coupling and the other is the downstream coupling 112B. Theupstream coupling 112A establishes fluid communication between theprinthead IC's 68 and the ink supply 60 (see FIG. 6) and the downstreamcoupling 112B connects to the sump 92 (refer FIG. 6 again).

The various elevations of the printhead cartridge 96 are shown in FIG.12. The plan view of the cartridge 96 also shows the location of thesection views shown in FIGS. 14, 15 and 16.

FIG. 13 is an exploded perspective of the cartridge 96. The LCP molding64 attaches to the underside of the cartridge chassis 100. In turn theflex PCB 108 attaches to the underside of the LCP molding 64 and wrapsaround one side to expose the printhead contacts 104. An inlet manifoldand filter 116 and outlet manifold 118 attach to the top of the chassis100. The inlet manifold and filter 116 connects to the LCP inlets 122via elastomeric connectors 120. Likewise the LCP outlets 124 connect tothe outlet manifold 118 via another set of elastomeric connectors 120.The chassis lid 102 encases the inlet and outlet manifolds in thechassis 100 from the top and the removable protective cover 98 snapsover the bottom to protect the contacts 104 and the printhead IC's (seeFIG. 11).

Inlet and Filter Manifold

FIG. 14 is an enlarged section view taken along line 14-14 of FIG. 12.It shows the fluid path through one of the cartridge valves 114 of theupstream coupling 112A to the LCP molding 64. The cartridge valve 114has an elastomeric sleeve 126 that is biased into sealing engagementwith a fixed valve member 128. The cartridge valve 114 is opened by theprinter conduit 142 (see FIG. 16) by compressing the elastomeric sleeve126 such that it unseats from the fixed valve member 128 and allows inkto flow up to a roof channel 138 along the top of the inlet and filtermanifold 116. The roof channel 138 leads to an upstream filter chamber132 that has one wall defined by a filter membrane 130. Ink passesthrough the filter membrane 130 into the downstream filter chamber 134and out to the LCP inlet 122. From there filtered ink flows along theLCP main channels 136 to feed into the printhead IC's (not shown).

Particular features and advantages of the inlet and filter manifold 116will now be described with reference to FIG. 15. The explodedperspective of FIG. 15 best illustrates the compact design of the inletand filter manifold 116. There are several aspects of the design thatcontribute to its compact form. Firstly, the cartridge valves are spacedclose together. This is achieved by departing from the traditionalconfiguration of self-sealing ink valves. Previous designs also used anelastomeric member biased into sealing engagement with a fixed member.However, the elastomeric member was either a solid shape that the inkwould flow around, or in the form of a diaphragm if the ink flowedthrough it.

In a cartridge coupling, it is highly convenient for the cartridgevalves to automatically open upon installation. This is most easily andcheaply provided by a coupling in which one valve has an elastomericmember which is engaged by a rigid member on the other valve. If theelastomeric member is in a diaphragm form, it usually holds itselfagainst the central rigid member under tension. This provides aneffective seal and requires relatively low tolerances. However, it alsorequires the elastomer element to have a wide peripheral mounting. Thewidth of the elastomer will be a trade-off between the desired couplingforce, the integrity of the seal and the material properties of theelastomer used.

As best shown in FIG. 16, the cartridge valves 114 use elastomericsleeves 126 that seal against the fixed valve member 128 under residualcompression. The valve 114 opens when the cartridge is installed in theprinter and the conduit end 148 of the printer valve 142 furthercompresses the sleeve 126. The collar 146 unseals from the fixed valvemember 128 to connect the LCP 64 into the printer fluidic system (seeFIG. 6) via the upstream and downstream ink coupling 112A and 112B. Thesidewall of the sleeve is configured to bulge outwardly as collapsinginwardly can create a flow obstruction. As shown in FIG. 16, the sleeve126 has a line of relative weakness around its mid-section that promotesand directs the buckling process. This reduces the force necessary toengage the cartridge with the printer, and ensures that the sleevebuckles outwardly.

The coupling is configured for ‘no-drip’ disengagement of the cartridgefrom the printer. As the cartridge is pulled upwards from the printerthe elastomeric sleeve 126 pushes the collar 146 to seal against thefixed valve member 128. Once the sleeve 126 has sealed against the valvemember 128 (thereby sealing the cartridge side of the coupling), thesealing collar 146 lifts together with the cartridge. This unseals thecollar 146 from the end of the conduit 148. As the seal breaks an inkmeniscus forms across the gap between the collar and the end of theconduit 148. The shape of the end of the fixed valve member 128 directsthe meniscus to travel towards the middles of its bottom surface insteadof pinning to a point. At the middle of the rounded bottom of the fixedvalve member 128, the meniscus is driven to detach itself from the nowalmost horizontal bottom surface. To achieve the lowest possible energystate, the surface tension drives the detachment of the meniscus fromthe fixed valve member 128. The bias to minimize meniscus surface areais strong and so the detachment is complete with very little, if any,ink remaining on the cartridge valve 114. Any remaining ink is notenough a drop that can drip and stain prior to disposal of thecartridge.

When a fresh cartridge is installed in the printer, the air in conduit150 will be entrained into the ink flow 152 and ingested by thecartridge. In light of this, the inlet manifold and filter assembly havea high bubble tolerance. Referring back to FIG. 15, the ink flowsthrough the top of the fixed valve member 128 and into the roof channel138. Being the most elevated point of the inlet manifold 116, the roofchannels can trap the bubbles. However, bubbles may still flow into thefilter inlets 158. In this case, the filter assembly itself is bubbletolerant.

Bubbles on the upstream side of the filter member 130 can affect theflow rate—they effectively reduce the wetted surface area on the dirtyside of the filter membrane 130. The filter membranes have a longrectangular shape so even if an appreciable number of bubbles are drawninto the dirty side of the filter, the wetted surface area remains largeenough to filter ink at the required flow rate. This is crucial for thehigh speed operation offered by the present invention.

While the bubbles in the upstream filter chamber 132 can not cross thefilter membrane 130, bubbles from outgassing may generate bubbles in thedownstream filter chamber 134. The filter outlet 156 is positioned atthe bottom of the downstream filter chamber 134 and diagonally oppositethe inlet 158 in the upstream chamber 132 to minimize the effects ofbubbles in either chamber on the flow rate.

The filters 130 for each color are vertically stacked closelyside-by-side. The partition wall 162 partially defines the upstreamfilter chamber 132 on one side, and partially defines the downstreamchamber 134 of the adjacent color on the other side. As the filterchambers are so thin (for compact design), the filter membrane 130 canbe pushed against the opposing wall of the downstream filter chamber134. This effectively reduces the surface are of the filter membrane130. Hence it is detrimental to maximum flowrate. To prevent this, theopposing wall of the downstream chamber 134 has a series of spacer ribs160 to keep the membrane 130 separated from the wall.

Positioning the filter inlet and outlet at diagonally opposed cornersalso helps to purge the system of air during the initial prime of thesystem.

To reduce the risk of particulate contamination of the printhead, thefilter membrane 130 is welded to the downstream side of a firstpartition wall before the next partition wall 162 is welded to the firstpartition wall. In this way, any small pieces of filter membrane 130that break off during the welding process, will be on the ‘dirty’ sideof the filter 130.

LCP Molding/Flex PCB/Printhead ICs

The LCP molding 64, flex PCB 108 and printhead ICs 68 assembly are shownin FIGS. 17 to 33. FIG. 17 is a perspective of the underside of the LCPmolding 64 with the flex PCB and printhead ICs 68 attached. The LCPmolding 64 is secured to the cartridge chassis 100 through coutersunkholes 166 and 168. Hole 168 is an obround hole to accommodate any missmatch in coefficients of thermal expansion (CTE) without bending theLCP. The printhead ICs 68 are arranged end to end in a line down thelongitudinal extent of the LCP molding 64. The flex PCB 108 is wirebonded at one edge to the printhead ICs 68. The flex PCB 108 alsosecures to the LCP molding at the printhead IC edge as well as at thecartridge contacts 104 edge. Securing the flex PCB at both edges keepsit tightly held to the curved support surface 170 (see FIG. 19). Thisensures that the flex PCB does not bend to a radius that is tighter thanspecified minimum, thereby reducing the risk that the conductive tracksthrough the flex PCB will fracture.

FIG. 18 is an enlarged view of Inset A shown in FIG. 17. It shows theline of wire bonding contacts 164 along the side if the flex PCB 108 andthe line of printhead ICs 68.

FIG. 19 is an exploded perspective of the LCP/flex/printhead IC assemblyshowing the underside of each component. FIG. 20 is another explodedperspective, this time showing the topside of the components. The LCPmolding 64 has an LCP channel molding 176 sealed to its underside. Theprinthead ICs 68 are attached to the underside of the channel molding176 by adhesive IC attach film 174. On the topside of the LCP channelmolding 176 are the LCP main channels 184. These are open to the inkinlet 122 and ink outlet 124 in the LCP molding 64. At the bottom of theLCP main channels 184 are a series of ink supply passages 182 leading tothe printhead ICs 68. The adhesive IC attach film 174 has a series oflaser drilled supply holes 186 so that the attachment side of eachprinthead IC 68 is in fluid communication with the ink supply passages182. The features of the adhesive IC attach film are described in detailbelow with reference to FIG. 31 to 33.

The LCP molding 64 has recesses 178 to accommodate electronic components180 in the drive circuitry on the flex PCB 108. For optimal electricalefficiency and operation, the cartridge contacts 104 on the PCB 108should be close to the printhead ICs 68. However, to keep the paper pathadjacent the printhead straight instead of curved or angled, thecartridge contacts 104 need to be on the side of the cartridge 96. Theconductive paths in the flex PCB are known as traces. As the flex PCBmust bend around a corner, the traces can crack and break theconnection. To combat this, the trace can be bifurcated prior to thebend and then reunited after the bend. If one branch of the bifurcatedsection cracks, the other branch maintains the connection.Unfortunately, splitting the trace into two and then joining it togetheragain can give rise to electromagnetic interference problems that createnoise in the circuitry.

Making the traces wider is not an effective solution as wider traces arenot significantly more crack resistant. Once the crack has initiated inthe trace, it will propagate across the entire width relatively quicklyand easily. Careful control of the bend radius is more effective atminimizing trace cracking, as is minimizing the number of traces thatcross the bend in the flex PCB.

Pagewidth printheads present additional complications because of thelarge array of nozzles that must fire in a relatively short time. Firingmany nozzles at once places a large current load on the system. This cangenerate high levels of inductance through the circuits which can causevoltage dips that are detrimental to operation. To avoid this, the flexPCB has a series of capacitors that discharge during a nozzle firingsequence to relieve the current load on the rest of the circuitry.Because of the need to keep a straight paper path past the printheadICs, the capacitors are traditionally attached to the flex PCB near thecontacts on the side of the cartridge. Unfortunately, they createadditional traces that risk cracking in the bent section of the flexPCB.

This is addressed by mounting the capacitors 180 (see FIG. 20) closelyadjacent the printhead ICs 68 to reduce the chance of trace fracture.The paper path remains linear by recessing the capacitors and othercomponents into the LCP molding 64. The relatively flat surface of theflex PCB 108 downstream of the printhead ICs 68 and the paper shield 172mounted to the ‘front’ (with respect to the feed direction) of thecartridge 96 minimize the risk of paper jams.

Isolating the contacts from the rest of the components of the flex PCBminimizes the number of traces that extend through the bent section.This affords greater reliability as the chances of cracking reduce.Placing the circuit components next to the printhead IC means that thecartridge needs to be marginally wider and this is detrimental tocompact design. However, the advantages provided by this configurationoutweigh any drawbacks of a slightly wider cartridge. Firstly, thecontacts can be larger as there are no traces from the componentsrunning in between and around the contacts. With larger contacts, theconnection is more reliable and better able to cope with fabricationinaccuracies between the cartridge contacts and the printer-sidecontacts. This is particularly important in this case, as the matingcontacts rely on users to accurately insert the cartridge.

Secondly, the edge of the flex PCB that wire bonds to the side of theprinthead IC is not under residual stress and trying to peel away fromthe bend radius. The flex can be fixed to the support structure at thecapacitors and other components so that the wire bonding to theprinthead IC is easier to form during fabrication and less prone tocracking as it is not also being used to anchor the flex.

Thirdly, the capacitors are much closer to the nozzles of the printheadIC and so the electromagnetic interference generated by the dischargingcapacitors is minimized.

FIG. 21 is an enlargement of the underside of the printhead cartridge 96showing the flex PCB 108 and the printhead ICs 68. The wire bondingcontacts 164 of the flex PCB 108 run parallel to the contact pads of theprinthead ICs 68 on the underside of the adhesive IC attach film 174.FIG. 22 shows FIG. 21 with the printhead ICs 68 and the flex PCB removedto reveal the supply holes 186. The holes are arranged in fourlongitudinal rows. Each row delivers ink of one particular color andeach row aligns with a single channel in the back of each printhead IC.

FIG. 23 shows the underside of the LCP channel molding 176 with theadhesive IC attach film 174 removed. This exposes the ink supplypassages 182 that connect to the LCP main channels 184 (see FIG. 20)formed in the other side of the channel molding 176. It will beappreciated that the adhesive IC attach film 174 partly defines thesupply passages 182 when it is stuck in place. It will also beappreciated that the attach film must be accurately positioned, as theindividual supply passages 182 must align with the supply holes 186laser drilled through the film 174.

FIG. 24 shows the underside of the LCP molding with the LCP channelmolding removed. This exposes the array of blind cavities 200 thatcontain air when the cartridge is primed with ink in order to damp anypressure pulses. This is discussed in greater detail below.

Printhead IC Attach Film

Laser Ablated Film

Turning briefly to FIGS. 31 to 33, the adhesive IC attachment film isdescribed in more detail. The film 174 may be laser drilled and woundonto a reel 198 for convenient incorporation in the printhead cartridge96. For the purposes of handling and storage, the film 174 has twoprotective liners (typically PET liners) on either side. One is anexisting liner 188B that is already attached to the film prior to laserdrilling. The other is a replacement liner 192, which replaces anexisting liner 188A, after the drilling operation.

The section of the laser-drilled film 174 shown in FIG. 32 has some ofthe existing liner 188B removed to expose the supply holes 186. Thereplacement liner 192 on the other side of the film replaces an existingliner 188A after the supply holes 186 have been laser drilled.

FIGS. 33A to 33C show in detail how the film 174 is manufactured bylaser ablation. FIG. 33A shows in detail the laminate structure of thefilm prior to laser-drilling. The central web 190 is typically apolyimide film and provides the strength for the laminate. The web 190is sandwiched between first and second adhesive layers 194A and 194B,which are typically epoxy layers. The first adhesive layer 194A is forbonding to the LCP channel molding 176. The second adhesive layer 194Bis for bonding to the printhead ICs 68. The first adhesive layer 194Atypically has a melt temperature which is at least 10° C. less than themelt temperature of the second adhesive layer 194B. As described in moredetail below, this difference in melt temperatures improves control ofthe printhead IC attachment process and, consequently, improves theperformance of the film 174 in use.

For the purposes of film storage and handling, each adhesive layer 194Aand 194 B is covered with a respective liner 188A and 188B. The centralweb 190 typically has a thickness of from 20 to 100 microns (usuallyabout 50 microns). Each adhesive layer 194A and 194B typically has athickness of from 10 to 50 microns (usually about 25 microns).

Referring to FIG. 33B, laser-drilling is performed from the side of thefilm defined by the liner 188A. A hole 186 is drilled through the firstliner 188A, the epoxy layers 194A and 194B and the central web 190. Thehole 186 terminates somewhere in the liner 188B, and so the liner 188Bmay be thicker than the liner 188A (e.g. liner 188A may be 10-20 micronsthick; liner 188B may be 30-100 microns thick).

The foraminous liner 188A on the laser-entry side is then removed andreplaced with a replacement liner 192, to provide the film package shownin FIG. 33C. This film package is then wound onto a reel 198 (see FIG.31) for storage and handling prior to attachment. When the printheadcartridge is assembled, suitable lengths are drawn from the reel 198,the liners removed, and the film 174 adhered to the underside of the LCPchannel molding 176 such that the holes 186 are in registration with thecorrect ink supply passages 182 (see FIG. 25).

Laser drilling is a standard method for defining holes in polymer films.However, a problem with laser drilling is that it deposits acarbonaceous soot 197 in and around the drilling site (see FIGS. 33B and33C). Soot around a protective liner may be easily dealt with, becausethis is usually replaced after laser drilling. However, soot 197deposited in and around the actual supply holes 186 is potentiallyproblematic. When the film is compressed between the LCP channel molding176 and printhead ICs 68 during bonding, the soot may be dislodged. Anydislodged soot 197 represents a means by which particulates may enterthe ink supply system and potentially block nozzles in the printhead ICs68. Moreover, the soot is surprisingly fast and cannot be removed byconventional ultrasonication and/or IPA washing techniques.

From analysis of laser-drilled films 174, it has been observed by thepresent Applicants that the soot 197 is generally present on thelaser-entry side of the film 174 (i.e. the epoxy layer 194A and centralweb 190), but is usually absent from the laser-exit side of the film(i.e. the epoxy layer 194B).

Double-Pass Laser Ablated Film

In U.S. application Ser. No. 12/049,371 filed on Mar. 17, 2008, thecontent of which is incorporated herein by reference, the Applicantdescribed how double-pass laser ablation of the ink supply holes 186eliminates the majority of soot deposits 197, including those on thelaser-entry side of the film. The starting point for double-pass laserablation is the film shown in FIG. 33A.

In a first step, a first hole 185 is laser-drilled from the side of thefilm defined by the liner 188A. The hole 185 is drilled through theliner 188A, the epoxy layers 194A and 194B, and the central web 190. Thehole 185 terminates somewhere in the liner 188B. The first hole 185 hassmaller dimensions than the intended ink supply hole 186. Typically eachlength and width dimension of the first hole 185 is about 10 micronssmaller than the length and width dimensions of the intended ink supplyhole 186. It will be seen from FIG. 34A that the first hole 185 has soot197 deposited on the first liner 188A, the first epoxy layer 194A andthe central web 190.

In a second step, the first hole 185 is reamed by further laser drillingso as to provide the ink supply hole 186 having the desired dimensions.The reaming process generates very little soot and the resulting inksupply hole 186 therefore has clean sidewalls as shown in FIG. 34B.

Finally, and referring to FIG. 34C, the first liner 188A is replacedwith a replacement liner 192 to provide a film package, which is readyto be wound onto a reel 198 and used subsequently for attachingprinthead ICs 68 to the LCP channel molding 176. The second liner 188Bmay also be replaced at this stage, if desired.

Comparing the films shown in FIGS. 33C and 34C, it will be appreciatedthat the double laser ablation method provides a film 174 having muchcleaner ink supply holes 186 than simple laser ablation. Hence, the filmis highly suitable for attachment of printhhead ICs 68 to the LCPchannel molding 176, and does not contaminate ink with undesirable sootdeposits.

Printhead IC Attachment Process

Improvements in Die Attach Film 174

Referring to FIGS. 19 and 20, it will be appreciated that the printheadIC attachment process is a critical stage of printhead fabrication. Inthe IC attachment process, a first adhesive surface of the laser-drilledfilm 174 is initially bonded to the underside of LCP channel molding176, and then the printhead ICs 68 are subsequently bonded to anopposite second adhesive surface of the film 174. The film 174 hasepoxy-adhesive layers 194A and 194B on each side, which melt and bondunder the application of heat and pressure.

Since the LCP channel molding 176 has very poor thermal conductivity,application of heat during each of the bonding processes must beprovided via the second surface of the film 174, which is not in contactwith the LCP channel molding.

Control of the bonding processes is critical for optimal printheadperformance, both in terms of the positioning of each printhead IC 68and in terms of supply of ink to the printhead ICs. A typical sequenceof printhead IC attachment steps, using a prior art film 174 (asdescribed in US Publication No. 2007/0206056 incorporated herein byreference) is shown schematically in longitudinal section in FIGS.35A-D. Referring to FIG. 35A, the film 174 is initially aligned with LCPchannel molding 176 so that ink supply holes 186 are in properregistration with ink outlets defined in a manifold bonding surface 175.The ink outlets take the form of ink supply passages 182, as describedabove. The first adhesive layer 194A faces the manifold bonding surface175, whilst the opposite side of the film is protected with theprotective liner 188B.

Referring to FIG. 35B, bonding of the film 174 to the manifold bondingsurface 175 proceeds by applying heat and pressure from a heating block302. A silicone rubber pad 300 separates the heating block 302 from thefilm liner 188B so as to prevent any damage to the film 174 duringbonding. During bonding, the first epoxy layer 194A is heated to itsmelt temperature and bonds to the bonding surface 175 of the LCP channelmolding 176.

As shown in FIG. 35C, the liner 188B is then peeled from the film 174 toreveal the second epoxy layer 194B. Next, the printhead IC 68 is alignedwith the film 174 ready for the second bonding step. FIG. 35Cillustrates several problems, which are typically manifest in the firstbonding step. Since the epoxy layers 194A and 194B are identical inprior art films, both of these layers melt during the first bondingstep. Melting of the second epoxy layer 194B is problematic for manyreasons. Firstly, some of the epoxy adhesive 199 is squeezed out fromthe second epoxy layer 194B and lines the laser-drilled ink supply holes186. This decreases the area of the ink supply holes 186, therebyincreasing ink flow resistance in the completed printhead assembly. Insome cases, ink supply holes 186 may become completely blocked duringthe bonding process, which is very undesirable.

FIG. 36B shows an actual photograph of one of the ink supply holes 186suffering from the epoxy “squeeze-out” problem. Outer perimeter walls310 show the original dimensions of the laser drilled hole 186. Thelight-colored material 312 within the perimeter walls 310 is adhesive,which has squeezed into the ink supply hole 186 during bonding to theLCP channel molding 176. Finally, the central dark area defined byperimeter walls 314 shows the effective cross-sectional area of the inksupply hole 186 after bonding. In this example, the originallaser-drilled ink supply hole 186 has dimensions of 400 microns×130microns. After bonding and epoxy “squeeze-out”, these dimensions werereduced to 340 microns×80 microns. Notwithstanding the significantproblems of increased ink flow resistance, the blurred edges of the inksupply hole 186 are problematic for the second bonding step, because theprinthead ICs 68 must be aligned accurately with the ink supply holes186. In automated printhead fabrication, a specialized alignment deviceuses optical means to locate a centroid of each ink supply hole 186.Optical location of each centroid is made more difficult when edges ofeach ink supply hole 186 are blurred by squeezed-out epoxy.Consequently, alignment errors are more likely.

A second problem with the second epoxy layer 194B melting is that thefilm 174 loses some of its overall structural integrity. As aconsequence, the film 174 tends to billow or sag into the ink supplypassages 182 defined in the LCP channel molding 176. FIG. 35Cillustrates sagging portions 198 of the film 174 after the first bondingstep. The present Applicant has coined the term “tenting” to describethis phenomenon. “Tenting” is particularly problematic, because thebonding surface 195 of the second adhesive layer 194B loses itsplanarity. This loss of planarity is further exacerbated by thicknessvariations in the second adhesive layer 194B, resulting from the epoxy“squeeze-out” problem. The combination of “tenting” and thicknessvariations in the second adhesive layer 194B reduces the contact area ofits bonding surface 195, and leads to problems in the second bondingstep.

In the second bonding step, shown in FIG. 35D, each printhead IC 68 isheated to about 250° C. and then positioned accurately on the secondadhesive layer 194B. Accurate alignment of the printhead IC 68 with thefilm 174 ensures that the ink supply channel 218, in fluid communicationwith nozzles 69, is placed over its corresponding ink supply holes 186.One ink supply channel 218 is shown in longitudinal section in FIG. 35D,although it will be appreciated (from FIG. 25) that each printhead IC 68may have several rows of ink supply channels.

As a result of epoxy “squeeze-out”, the second adhesive layer 194B,having an original thickness of about 25 microns, may have its thicknessreduced to 5 to 10 microns in some regions. Such significant thicknessvariations in the second adhesive layer 194B can lead to skewedprinthead IC placement, in which one end of the printhead IC 68 israised relative to the other end. This is clearly undesirable andaffects print quality. A further problem with a non-planar bondingsurface 195 is that relatively long bonding times of about 5 seconds aretypically required, and each printhead IC 68 needs to be pressedrelatively far into the second adhesive layer 194B.

The most significant problem associated with printhead assemblies where“tenting” occurs in the adhesive film 174 is that the seal provided bythe film may be imperfect. The present Applicant has developed a leaktest to determine the effectiveness of the seal provided by the film 174in a printhead assembly. In this test, the printhead assembly isinitially soaked in ink at 90° C. for one week. After ink soaking andflushing, one color channel of the printhead assembly is then chargedwith air at 10 kPa, and the rate of air leakage from this color channelis measured. Leakages may occur by transfer of air to other colorchannels in the printhead (via the film 174) or by direct losses of airto the atmosphere. In this test, a typical printhead assembly fabricatedusing the IC attachment film described in US Publication No.2007/0206056 has a leakage rate of about 300 mm³ per minute or greater.

In light of the above-mentioned problems, the Applicant has developed animproved printhead IC attachment process, which minimizes theseproblems. The improved printhead IC attachment process is described inU.S. application Ser. No. 12/049,373 filed on Mar. 17, 2008, thecontents of which is incorporated herein by reference. The improved ICattachment process follows essentially the same steps as those describedabove in connection with FIGS. 35A-D. However, the design of the film174 reduces the problems associated with the first bonding step and,equally importantly, reduces the consequential problems associated withthe second bonding step. The film 174 still comprises a centralpolymeric web 190 sandwiched between first and second adhesive layers194A and 194B. (For convenience, corresponding parts of the film 174have the same labels used in the preceding description). However, incontrast with previous film designs, the first and second epoxy layers194A and 194B are differentiated in the film. In particular, the epoxylayer 194A has a melt temperature, which is at least 10° C. less thanthe melt temperature of the second epoxy layer 194B. Typically, thedifference in melt temperatures is at least 20° C. or at least 30° C.For example, the first epoxy layer 194A may have a melt temperature inthe range of 80 to 130° C., whilst the second epoxy layer may have amelt temperature in the range of 140 to 180° C. The skilled person willreadily be able to select adhesive films (e.g. epoxy films) meetingthese criteria. Suitable adhesive films for use in the laminate film 174are Hitachi DF-XL9 epoxy film (having a melt temperature of about 120°C.) and Hitachi DF-470 epoxy film (having a melt temperature of about160° C.).

Accordingly, the first bonding step (illustrated by FIG. 35B) can becontrolled so that no melting of the second adhesive layer 194B occursduring bonding of the first adhesive layer 194A to the bonding surface195 of the LCP channel molding 176. Typically, the temperature of theheating block 302 matches the melt temperature of the first adhesivelayer 194A. Consequently, “squeeze-out” of the first adhesive layer isminimized or eliminated altogether. Furthermore, minimal or no “tenting”occurs during the bonding process.

Referring to FIG. 37A, there is shown a bonded LCP/film assembly usingthe film 174. In contrast with the assembly shown in FIG. 35C, it can beseen that no “tenting” in the film 174 has occurred, and that the secondadhesive layer 194B has uniform planarity and thickness. FIG. 36A showsan actual photograph of one of the ink supply holes 186 after bonding tothe LCP channel molding 176 using the film 174. The definition of theink supply hole 186 is dramatically improved compared to the ink supplyhole shown in FIG. 36B, and it can be seen that no epoxy “squeeze-out”has occurred. Consequently, there is no undesirable increase in ink flowresistance through the hole shown in FIG. 36A, and optical location ofthe hole's centroid can be performed with minimal errors.

Moreover, with the problems associated with the first bonding stepminimized, the consequential problems associated with the second bondingstep are also minimized. As shown in FIG. 37A, the second adhesive layer194B has a planar bonding surface 195, and has minimal thicknessvariations. Accordingly, printhead IC placement and bonding issignificantly improved, with the result that relatively short bondingtimes of about 1 second can be employed. The planar bonding surface 195shown in FIG. 37A also means that printhead ICs 68 do not need to bepressed far into the second adhesive layer 194B to provide sufficientbonding strength, and skewed printhead ICs 68 are less likely to resultfrom the attachment process.

Referring to FIG. 37B, the printhead assembly resulting from theimproved printhead IC attachment process has excellent seals around eachink supply hole 186, largely as a result of the absence of “tenting” andepoxy “squeeze-out”. In the Applicant's leak tests described above, theprinthead assembly shown in FIG. 37B exhibited a remarkable 3000-foldimprovement compared to the printhead assembly shown in FIG. 35D. Aftersoaking in ink at 90° C. for one week, the measured leakage rate for theprinthead assembly shown in FIG. 37B was about 0.1 mm³ per minute, whencharged with air at 10 kPa.

Improvements in the LCP Channel Molding 176

As described above, the IC attachment process involves bonding a firstadhesive surface of the laser-drilled film 174 to the underside of theLCP channel molding 176. Subsequently, the printhead ICs 68 are bondedto an opposite second adhesive surface of the film 174. Although theabove-mentioned improvements in the film 174 help to minimize inkleakages from the bond between the LCP channel molding 176 and theprinthead ICs 68, molding irregularities in the LCP channel molding 176can still provide a source of undesirable ink leakages. In particular,microscopic molding fissures (e.g. cracks, grooves, indentations, voidsetc) in the LCP channel molding 176 can have a deleterious effect on theseal between the LCP channel molding and the printhead ICs 68. Thesemolding fissures are potential sources of ink leakage.

As shown in FIG. 38, molding fissures 350 (shown exaggerated forclarity) may occur at the bonding surface of the LCP channel molding 176and/or internally between ink supply passages 182. In either case, inkleakages and/or color mixing may result if the fissures 350 are notplugged or otherwise sealed by the IC attachment process.

FIG. 39 shows a process whereby the LCP channel molding 176 is coatedwith a polymer coating 352. Before attaching any printhead ICs 68, theentire LCP molding 64 (which includes the LCP channel molding 176 sealedto its underside), is dipped in a polymer coating solution 354. Thisresults in a coated LCP channel molding in which all fissures 350 areplugged with the polymer coating 352. Plugging of surface fissures withthe polymer coating 352 improves the profile of the bonding surface 175,which is to be bonded to one side of the adhesive film 174. Inparticular, by minimizing surface unevenness, the resultant bondedprinthead assembly, as shown in FIG. 40, has an improved seal betweenthe LCP channel molding 174 and the adhesive film 174.

Furthermore, plugging of internal fissures in the LCP channel molding176 minimizes any cross-color contamination within the LCP channelmolding.

The polymer coating 352 may be applied using any suitable process, suchas dipping, spray coating or spin coating. As shown in FIG. 39, theentire LPC molding 64 is dipped in the polymer coating solution, whichcomprises a polymer dispersed or dissolved in suitable solvent (e.g.organic solvent). The polymer may be curable upon drying, application ofheat, or exposure to UV.

The polymer coating may comprise any suitable polymer, such aspolyimides, polyesters (e.g. PET), epoxies, polyolefins (e.g.polyethylene, polypropylene, PTFE), siloxanes (e.g. PDMS) or liquidcrystal polymers. Combinations of polymers and/or copolymers may also beused as suitable coating polymers. Usually, the polymer coatingcomprises a different polymer material than the LCP channel molding 176.

Furthermore, the polymer coating 352 may be selected, or may containadditives, to provide the LCP channel molding 176 with desirable surfacecharacteristics. For example, the polymer coating may comprise anadhesive additive to improve bonding to the film 174. Alternatively (oradditionally), the polymer coating may comprise additives to improvesurface characteristics of the ink supply passages e.g. increasedwettability. Alternatively (or additionally), the polymer coating maycomprise additives to improve the overall durability of the LCP channelmolding 176 e.g. anti-scratch additives, such as silica particles.

Enhanced Ink Supply to Printhead IC Ends

FIG. 25 shows the printhead ICs 68, superimposed on the ink supply holes186 through the adhesive IC attach film 174, which are in turnsuperimposed on the ink supply passages 182 in the underside of the LCPchannel molding 176. Adjacent printhead ICs 68 are positioned end to endon the bottom of the LCP channel molding 176 via the attach film 174. Atthe junction between adjacent printhead ICs 68, one of the ICs 68 has a‘drop triangle’ 206 portion of nozzles in rows that are laterallydisplaced from the corresponding row in the rest of the nozzle array220. This allows the edge of the printing from one printhead IC to becontiguous with the printing from the adjacent printhead IC. Bydisplacing the drop triangle 206 of nozzles, the spacing (in a directionperpendicular to media feed) between adjacent nozzles remains unchangedregardless of whether the nozzles are on the same IC or either side ofthe junction on different ICs. This requires precise relativepositioning of the adjacent printhead ICs 68, and the fiducial marks 204are used to achieve this. The process can be time consuming but avoidsartifacts in the printed image.

Unfortunately, some of the nozzles at the ends of a printhead IC 68 canbe starved of ink relative to the bulk of the nozzles in the rest of thearray 220. For example, the nozzles 222 can be supplied with ink fromtwo ink supply holes. Ink supply hole 224 is the closest. However, ifthere is an obstruction or particularly heavy demand from nozzles to theleft of the hole 224, the supply hole 226 is also proximate to thenozzles at 222, so there is little chance of these nozzles deprimingfrom ink starvation.

In contrast, the nozzles 214 at the end of the printhead IC 68 wouldonly be in fluid communication with the ink supply hole 216 were it notfor the ‘additional’ ink supply hole 210 placed at the junction betweenthe adjacent ICs 68. Having the additional ink supply hole 210 meansthat none of the nozzles are so remote from an ink supply hole that theyrisk ink starvation.

Ink supply holes 208 and 210 are both fed from a common ink supplypassage 212. The ink supply passage 212 has the capacity to supply bothholes as supply hole 208 only has nozzles to its left, and supply hole210 only has nozzles to its right. Therefore, the total flowrate throughsupply passage 212 is roughly equivalent to a supply passage that feedsone hole only.

FIG. 25 also highlights the discrepancy between the number of channels(colors) in the ink supply—four channels—and the five channels 218 inthe printhead IC 68. The third and fourth channels 218 in the back ofthe printhead IC 68 are fed from the same ink supply holes 186. Thesesupply holes are somewhat enlarged to span two channels 218.

The reason for this is that the printhead IC 68 is fabricated for use ina wide range of printers and printhead configurations. These may havefive color channels—CMYK and IR (infrared)—but other printers, such thisdesign, may only be four channel printers, and others still may only bethree channel (CC, MM and Y). In light of this, a single color channelmay be fed to two of the printhead IC channels. The print enginecontroller (PEC) microprocessor can easily accommodate this into theprint data sent to the printhead IC. Furthermore, supplying the samecolor to two nozzle rows in the IC provides a degree of nozzleredundancy that can used for dead nozzle compensation.

Pressure Pulses

Sharp spikes in the ink pressure occur when the ink flowing to theprinthead is stopped suddenly. This can happen at the end of a print jobor a page. The Assignee's high speed, pagewidth printheads need a highflow rate of supply ink during operation. Therefore, the mass of ink inthe ink line to the nozzles is relatively large and moving at anappreciable rate.

Abruptly ending a print job, or simply at the end of a printed page,requires this relatively high volume of ink that is flowing relativelyquickly to come to an immediate stop. However, suddenly arresting theink momentum gives rise to a shock wave in the ink line. The LCP molding64 (see FIG. 19) is particularly stiff and provides almost no flex asthe column of ink in the line is brought to rest. Without any compliancein the ink line, the shock wave can exceed the Laplace pressure (thepressure provided by the surface tension of the ink at the nozzlesopenings to retain ink in the nozzle chambers) and flood the frontsurface of the printhead IC 68. If the nozzles flood, ink may not ejectand artifacts appear in the printing.

Resonant pulses in the ink occur when the nozzle firing rate matches aresonant frequency of the ink line. Again, because of the stiffstructure that define the ink line, a large proportion of nozzles forone color, firing simultaneously, can create a standing wave or resonantpulse in the ink line. This can result in nozzle flooding, or converselynozzle deprime because of the sudden pressure drop after the spike, ifthe Laplace pressure is exceeded.

To address this, the LCP molding 64 incorporates a pulse damper toremove pressure spikes from the ink line. The damper may be an enclosedvolume of gas that can be compressed by the ink. Alternatively, thedamper may be a compliant section of the ink line that can elasticallyflex and absorb pressure pulses.

To minimize design complexity and retain a compact form, the inventionuses compressible volumes of gas to damp pressure pulses. Dampingpressure pulses using gas compression can be achieved with small volumesof gas. This preserves a compact design while avoiding any nozzleflooding from transient spikes in the ink pressure.

As shown in FIGS. 24 and 26, the pulse damper is not a single volume ofgas for compression by pulses in the ink. Rather the damper is an arrayof cavities 200 distributed along the length of the LCP molding 64. Apressure pulse moving through an elongate printhead, such as a pagewidthprinthead, can be damped at any point in the ink flow line. However, thepulse will cause nozzle flooding as it passes the nozzles in theprinthead integrated circuit, regardless of whether it is subsequentlydissipated at the damper. By incorporating a number of pulse dampersinto the ink supply conduits immediately next to the nozzle array, anypressure spikes are damped at the site where they would otherwise causedetrimental flooding.

It can be seen in FIG. 26, that the air damping cavities 200 arearranged in four rows. Each row of cavities sits directly above the LCPmain channels 184 in the LCP channel molding 176. Any pressure pulses inthe ink in the main channels 184 act directly on the air in the cavities200 and quickly dissipate.

Printhead Priming

Priming the cartridge will now be described with particular reference tothe LCP channel molding 176 shown in FIG. 27. The LCP channel molding176 is primed with ink by suction applied to the main channel outlets232 from the pump of the fluidic system (see FIG. 6). The main channels184 are filled with ink and then the ink supply passages 182 andprinthead ICs 68 self prime by capillary action.

The main channels 184 are relatively long and thin. Furthermore the aircavities 200 must remain unprimed if they are to damp pressure pulses inthe ink. This can be problematic for the priming process which caneasily fill cavities 200 by capillary action or the main channel 184 canfail to fully prime because of trapped air. To ensure that the LCPchannel molding 176 fully primes, the main channels 184 have a weir 228at the downstream end prior to the outlet 232. To ensure that the aircavities 200 in the LCP molding 64 do not prime, they have openings withupstream edges shaped to direct the ink meniscus from traveling up thewall of the cavity.

These aspects of the cartridge are best described with reference FIGS.28A, 28B and 29A to 29C. These figures schematically illustrate thepriming process. FIGS. 28A and 28B show the problems that can occur ifthere is no weir in the main channels, whereas FIGS. 29A to 29C show thefunction of the weir 228.

FIGS. 28A and 28B are schematic section views through one of the mainchannels 184 of the LCP channel molding 176 and the line of air cavities200 in the roof of the channel. Ink 238 is drawn through the inlet 230and flows along the floor of the main channel 184. It is important tonote that the advancing meniscus has a steeper contact angle with thefloor of the channel 184. This gives the leading portion of the ink flow238 a slightly bulbous shape. When the ink reaches the end of thechannel 184, the ink level rises and the bulbous front contacts the topof the channel before the rest of the ink flow. As shown in FIG. 28B,the channel 184 has failed to fully prime, and the air is now trapped.This air pocket will remain and interfere with the operation of theprinthead. The ink damping characteristics are altered and the air canbe an ink obstruction.

In FIG. 29A to 29C, the channel 184 has a weir 228 at the downstreamend. As shown in FIG. 29A, the ink flow 238 pools behind the weir 228and rises toward the top of the channel. The weir 228 has a sharp edge240 at the top to act as a meniscus anchor point. The advancing meniscuspins to this anchor 240 so that the ink does not simply flow over theweir 228 as soon as the ink level is above the top edge.

As shown in FIG. 29B, the bulging meniscus makes the ink rise until ithas filled the channel 184 to the top. With the ink sealing the cavities200 into separate air pockets, the bulging ink meniscus at the weir 228breaks from the sharp top edge 240 and fills the end of the channel 184and the ink outlet 232 (see FIG. 29C). The sharp to edge 240 isprecisely positioned so that the ink meniscus will bulge until the inkfills to the top of the channel 184, but does not allow the ink to bulgeso much that it contacts part of the end air cavity 242. If the meniscustouches and pins to the interior of the end air cavity 242, it may primewith ink. Accordingly, the height of the weir and its position under thecavity is closely controlled. The curved downstream surface of the weir228 ensures that there are no further anchor points that might allow theink meniscus to bridge the gap to the cavity 242.

Another mechanism that the LCP uses to keep the cavities 200 unprimed isthe shape of the upstream and downstream edges of the cavity openings.As shown in FIGS. 28A, 28B and 29A to 29C, all the upstream edges have acurved transition face 234 while the downstream edges 236 are sharp. Anink meniscus progressing along the roof of the channel 184 can pin to asharp upstream edge and subsequently move upwards into the cavity bycapillary action. A transition surface, and in particular a curvedtransition surface 234 at the upstream edge removes the strong anchorpoint that a sharp edge provides.

Similarly, the Applicant's work has found that a sharp downstream edge236 will promote depriming if the cavity 200 has inadvertently filledwith some ink. If the printer is bumped, jarred or tilted, or if thefluidic system has had to reverse flow for any reason, the cavities 200may fully of partially prime. When the ink flows in its normal directionagain, a sharp downstream edge 236 helps to draw the meniscus back tothe natural anchor point (i.e. the sharp corner). In this way,management of the ink meniscus movement through the LCP channel molding176 is a mechanism for correctly priming the cartridge.

The invention has been described here by way of example only. Skilledworkers in this field will recognize many variations and modificationwhich do not depart from the spirit and scope of the broad inventiveconcept. Accordingly, the embodiments described and shown in theaccompanying figures are to be considered strictly illustrative and inno way restrictive on the invention.

1. A method of fabricating a printhead assembly, said method comprisingthe steps of: (i) providing a molded ink manifold having a manifoldbonding surface for attachment of one or more printhead integratedcircuits, said bonding surface having a plurality of ink outlets definedtherein, said bonding surface having a plurality of fissures resultingfrom a molding process; (ii) coating at least said manifold bondingsurface with a polymer coating, thereby plugging said fissures; and(iii) bonding one or more printhead integrated circuits to said manifoldbonding surface.
 2. The method of claim 1, wherein said manifold bondingsurface is substantially planar as a result of said polymer coatingplugging said fissures.
 3. The method of claim 1, wherein said coatingstep coats the entire molded ink manifold with said polymer coating. 4.The method of claim 1, wherein said polymer coating plugs internalfissures between ink supply passages defined in said ink manifold. 5.The method of claim 1, wherein said polymer coating is selected from thegroup of polymers consisting of: polyimides, polyesters, epoxies,polyolefins, siloxanes and liquid crystal polymers.
 6. The method ofclaim 1, wherein said polymer coating comprises inorganic or organicadditives for providing one or more of the following characteristics:wettability, adhesive bond strength, and scratch-resistance.
 7. Themethod of claim 1, wherein said coating step comprises any one of:dipping, spray coating or spin coating.
 8. The method of claim 7,wherein said coating step utilizes a polymer coating solution comprisingan organic solvent.
 9. The method of claim 7, wherein said coating stepis controlled to provide a polymer coating having a predeterminedthickness.
 10. The method of claim 1, wherein said bonding stepcomprises: bonding an adhesive film to said manifold bonding surface;and bonding said printhead integrated circuits to said adhesive film.11. The method of claim 10, wherein said adhesive film is a laminatedfilm comprising a central polymeric film sandwiched between first andsecond adhesive layers.